The present invention relates to rotary fluid pressure devices, and more particularly, to an improved thrust absorbing arrangement for use therein.
The invention is especially suited for use with hydraulic gerotor motors, a typical example of which is shown in U.S. Pat. No. 3,572,983, assigned to the assignee of the present invention. It has long been recognized that in such devices, there must be included some means for limiting the axial movement of the main drive shaft. Examples of such means are illustrated in U.S. Pat. No. 3,899,270, also assigned to the assignee of the present invention. In motors of the type shown in the first-referenced patent, because of the relatively low torques being transmitted by the main drive shaft, it was possible, by arrangements known in the art, to limit the axial movement of the main drive shaft in a manner which was generally satisfactory. However, it will be appreciated that as the torque output capability of such motors increased, the axial forces acting on the main drive shaft also increased, thus complicating the problem of satisfactory axial retention of the drive shaft.
More recently, the torque output capability of gerotor motors has been greatly increased by the development illustrated in U.S. Pat. No. 3,782,866, assigned to the assignee of the present invention. The basis for this development was the realization that the primary factor limiting the torque output capability of the motor was the strength of the spline connection between the rotor and the main shaft and between the main shaft and the output shaft. Thus, it is now well-known in the art to provide a high torque gerotor motor utilizing an intermediate shaft, one end of which is connected to the rotor of the gerotor by a set of straight splines, and the other end of which defines the relatively large set of internal splines. At the same time, the output shaft also defines a relatively large set of internal splines and a large dogbone shaft having external splines at either end thereof provides the main drive connection between the intermediate shaft and the output shaft.
With the increased size and strength of such spline connections, the torque output capability of this type of motor is now frequently in a range of 40,000-60,000 inch pounds. Because of unbalanced frictional forces in the various spline connections, output torques of the magnitude mentioned can frequently result in an axial force on the intermediate shaft in the range of about 10,000 pounds. This magnitude of axial resultant force may bias the intermediate shaft toward a rotating disc valve member for one rotational direction of operation, and in the opposite axial direction for the opposite rotational direction of operation, such that no force is acting on the disc valve.
An attempt has been made in the prior art to limit the axial movement of the intermediate shaft or main drive shaft, toward the disc valve member, by means of increasing the hydraulic force behind this valve member to maintain it in sealing contact with the adjacent port plate or housing portion. It will be appreciated, however, that this is not a satisfactory solution in the very high torque gerotor motors described above wherein it would be necessary to utilize such a high continuous biasing force which, when the axial force on the intermediate shaft was lower, or eliminated completely because of reversed operation, would still be applied to the disc valve member, producing an excessive load, friction and wear on the mating valve surfaces.
A different approach to limiting the axial movement of the main drive shaft is illustrated in U.S. Pat. No. 3,657,903, wherein the main drive shaft is provided with a shoulder having a rubbing surface which engages a mating rubbing surface on the adjacent, stationary valve member. In such an arrangement, a frictional force is developed as a result of the rubbing action between the mating wear surfaces, with the magnitude of such frictional forces being generally proportional to the torque output capacity of the device. Therefore, although the axial limiting arrangement of the above-referenced patent may be generally satisfactory for the relatively lower torque motors of the type shown in U.S. Pat. No. 3,572,983, such an arrangement is no longer satisfactory for use with relatively higher torque motors now available, and as taught in the '903 patent, the arrangement is not even applicable to the most recently developed motors such as those shown in U.S. Pat. No. 3,782,866.